Bredesen, Rolv
[excerpts]
What is in-cloud icing?
- If temperatures are below 0°C and the structure is located inside a cloud (above cloud base height) we get in-cloud icing.
- The ice accretion rates increases with the relative windspeed and the moisture content of the cloud.
- Because the blade of a wind turbine moves fast there is an elevated hazard associated with ice throw and fall from turbines located in icing conditions.
How far can the ice be thrown?
- Maximum throw distance (screening) : 1.5 × (Diam. + Ht.). ~ 350 m.*
- Ice debris have so far not been found at this distance.
- Ice pieces have been found at 68 % of the maximum throw distance.
- 1.4 × tip height (Cattin). 1000 ice pieces with 3 % above tip height
- 1 × tip height (Lunden, 2017). 500 ice pieces total.
*Strict German/Austrian regulations
- Seifert screening formula of danger zone: (Hubheiht + rotordiameter) × 1.5
- In Germany/Austria it is required to have ice detection systems if there are roads or buildings within this distance.
- Restriction on production: turbine must stop when there is icing.
- If detection systems are reliable and sensitive, then the potential hazard is most likely associated with ice fall and not throw of smaller ice pieces.
How dangerous is the ice?
- An impact kinetic energy of more than 40 J is considered fatal.
- 40 J correpsonds to a 0.2 kg ice piece with density 500 g/dm3 falling from an elevation of 30–50 m.
- Because of the turbine height all ice pieces larger than approximately 0.2 kg are potentially fatal.
How large a risk can we accept?
Localized individual risk metric: the probability that an average unprotected person, permanently present at a specified location, is killed in a period of one year due to an accident at a hazardous installation
Acceptable risk:
- Ski tracks, hiking areas < 10−4
- People walking along public road, industrial sites, scattered houses < 10−5
- Houses, cafés, shops, etc. < 10−6
- Schools, kindergartens, shopping malls, hospitals, etc. < 10−7
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See also: R.E. Bredesen, H. Farid, M. Pedersen, D. Haaheim, S. Rissanen, G. Gruben and A. Sandve, “IceRisk: Assessment of risks associated with ice throw from wind turbine blades” (PO.339). https://windeurope.org/summit2016/conference/allposters/PO339.pdf [3], in WindEurope Summit, Hamburg, 2016.
Rolv Erlend Bredesen, Kjeller Vindteknikk
IEA Wind Task 19, Winterwind 2017
February 15, 2017
Download original document: “Ice throw from wind turbines: Assessment and risk management [4]”
URL to article: https://www.wind-watch.org/documents/ice-throw-from-wind-turbines-assessment-and-risk-management/
URLs in this post:
[1] Image: https://docs.wind-watch.org/falling-ice-hazard.png
[2] Image: https://docs.wind-watch.org/risk-ice-injury.png
[3] https://windeurope.org/summit2016/conference/allposters/PO339.pdf: https://docs.wind-watch.org/ice-risk-poster.pdf
[4] Ice throw from wind turbines: Assessment and risk management: https://docs.wind-watch.org/ice_throw_from_wind_turbine_blades.pdf
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